Marine rescue craft, such as lifeboats, are usually launched in rough seas. Launching may take place either from a larger marine vessel, or a drilling platform, or other structure. In the great majority of cases launching devices for such rescue craft have been in the form of rope or cable hoists, and swingable crane-like arms. The hazards involved in launching rescue craft by means of such hoisting systems are too well-known to require description. It is, however, self-evident that launching of such rescue craft is likely to be required in periods of the very worst weather conditions. The difficulties in launching such craft increase in proportion to the severity of the weather, and in particular to the wave action.
One of the principal factors contributing to the hazardous nature of the launching operation is that the rescue craft will be located closely alongside the vessel or platform from which it is being launched until such time as it is released. Once it is released it must then attempt to get underway and head away from the parent vessel.
The difficulty involved in these operations is of course greatly increased where the parent vessel is listing, and launching is taking place from the "high" side of the vessel.
Clearly, it is desirable to provide a launching system for a rescue craft by means of which the rescue craft is carried away from the vessel during launching, and is in fact projected in such a manner that it carries a certain amount of weigh whereby once it reaches the water, it will move immediately and directly away from the parent vessel and also from the launching system itself.
In addition, it is desirable to provide a launching system which is self-regulating, and which can be operated from a listing vessel with substantially equal effect, either from the high or the low side.